Obsidian is a distinctive natural glass, formed by geological processes. Its unique appearance, characterized by a smooth, often dark, and reflective surface, has captivated people for centuries. This volcanic material continues to draw interest from collectors and those curious about Earth’s formations.
How Obsidian Forms
Obsidian is a natural glass, not a true mineral, formed from volcanic activity. It originates when silica-rich lava cools rapidly without sufficient time for crystals to grow. The lava’s high silica content contributes to its high viscosity, meaning it is thick and flows slowly.
This rapid cooling often occurs when molten lava encounters cooler air or water at the Earth’s surface, or along the edges of a lava flow or volcanic dome. The swift transition from a liquid to a solid state traps the atomic structure in a disordered, glass-like arrangement. This process results in obsidian’s tendency to fracture with smooth, curved, shell-like surfaces, known as conchoidal fractures, which produce very sharp edges.
Prime Locations for Obsidian Discovery
Obsidian is found in areas with a history of volcanic activity, particularly where rhyolitic eruptions have occurred. Notable global locations include:
- Mount Hekla in Iceland
- The Eolie Islands (e.g., Lipari) in Italy
- Milos and Gyali in Greece
- Acıgöl and Mount Ararat in Turkey
- Japan
- New Zealand
- Kenya
- Mexico
- Guatemala
- Argentina
- Chile
Within the United States, obsidian is widely distributed in the western states, reflecting their extensive volcanic past. Oregon is home to well-known sites like Glass Buttes, which offers varieties such as black, rainbow, mahogany, and gold sheen obsidian. The Big Obsidian Flow within Newberry National Volcanic Monument is another significant site, though collecting may be restricted inside monument boundaries.
California also has abundant obsidian, with locations like Modoc National Forest, which includes the historic Davis Creek obsidian flow, and the Warner Mountains, known for rainbow and pink obsidian. Other regions in the U.S. include the San Francisco Volcanic Field in Arizona, Craters of the Moon in Idaho, and areas in New Mexico and Utah. Yellowstone National Park in Wyoming features Obsidian Cliff, though collecting within the park is generally not permitted.
Identifying and Collecting Safely
Identifying obsidian in the field involves recognizing its distinct characteristics. It typically possesses a glossy, smooth, and reflective surface, resembling glass. When broken, obsidian exhibits a conchoidal fracture, creating very sharp edges. While commonly black, obsidian can also appear in various colors, including brown, red, green, or display patterns like snowflake, gold sheen, or rainbow effects, depending on impurities or microscopic inclusions.
When planning to collect obsidian, safety and ethical considerations are important. Given its sharp edges, wearing sturdy gloves and eye protection is important to prevent cuts. Robust footwear is also advised for navigating rough terrain. Tools such as a rock hammer or small shovel can assist in extraction, and soft material like newspaper or cloth is useful for wrapping specimens to prevent damage during transport.
It is important to determine land ownership before collecting, as rules vary significantly between private and public lands. It is also advisable to research local regulations before visiting any site. Collecting is generally prohibited in national parks, but some Bureau of Land Management (BLM) areas allow it, often with specific limits on quantity. Collectors should strive to minimize their environmental impact by staying on designated trails, filling any holes created, and packing out all trash. Respecting wildlife and adhering to local regulations helps ensure the preservation of collecting sites for others.